1. Field of Invention
The present invention relates to a construction technique for charging an improvement material such as a grout or the like into a soft ground through a vast number of points.
2. Related Art
As is known, in Japan which is small country and has a special landform in which a large number of mountains, forests and fields lie adjacent to complicatedly mixed coastline in which a large number of mountains, forests and fields, and flat land which can be utilized not only for farming and cattle breeding, but also for housing, constructing various industrial institutions, schools, hospitals, laboratories is limited. Therefore, it is an extremely important problem for a long time in Japan to effectively utilize the land. For this purpose, in order to spread the flat land which can be effectively utilized, searches and developments have been made for reclaiming valleys such as rivers, lakes and marshes, as well as soft grounds such as around shallow sea shores, for improving grounds for effectively utilizing the above described areas. Recently, practical results have been obtained, and some of them have been put to practical use.
Ground improving methods of construction such as sand drain and calcium oxide were used in times past, but they were complicated and expensive. Therefore, a ground improving method of construction has been widely used recently as shown in FIG. 21 in which a casing pipe is directly passed into the ground. An improving material such as grout is ejected and charged into the ground from a predetermined ejection port formed in the casing pipe during a process or the like for pulling up the improving material from a predetermined depth while rotating the casing pipe, and the improving material is concreted in the ground to form the improved area with passage of time. In the ground improving method of construction of the above described type, an insertion apparatus 3 allows the casing pipe 2 to bore and pass into the ground 1. A grout 9 which is the predetermined improving material is pumped into the casing pipe 2 through a swivel joint 7 from a grout tank 6 by a single-cylinder pump 5 which is controlled and driven by a generator 4. Also during the process of pulling the casing pipe 2, the grout 9 is ejected and charged into the ground 1 from a nozzle type ejection port 8 formed at a tip end of the casing pipe 2, thereby improving the ground.
Various improvements and developments have been repeatedly made. These improvements include ejecting and charging the grout of the above type into the ground 1 using a so-called double-pipe double-packer charging method as shown in FIG. 22. This includes a technique in which an antecedent bore 10 is formed in the ground by a casing pipe, and an inner pipe 12 made of synthetic resin or the like having a sleeve 11 coaxially fitted therearound is inserted into the antecedent bore 10. A sealing mortar 13 or the like is charged between the inner pipe 12 and the antecedent bore 10, and packers 14 and 14 are disposed in the inner pipe 12 at a predetermined pitch to contact the packers 14 and 14, contact an inner surface of the inner pipe 12 under pressure. A predetermined improving material 9 such as grout is pumped from a grout tank 6 by pumps 5' between the packers 14 and 14, and the improving material 9 is ejected and charged from an ejection port 8 of the inner pipe 12 through a slit of the sleeve 11 and the sealing mortar 13, thereby constructing a predetermined improved area.
As such a double-pipe double-packer charging method, a so-called strainer pipe charging method and a Soletanshu charging method are known.
In the conventional methods for ejection and charging the improving material 9 into the ground 1 as shown in FIGS. 21 and 22, since the improving material 9 is ejected from a spot-like ejection port by the pumps 5 and 5', and since a nozzle diameter of the ejection port 8 is small, a dynamic pressure of the improving material ejected from the ejection port 8 becomes high, and a crack is generated in the ground 1 of the improved area around the ejected improving material 9. Additionally there are drawbacks that the ground 1 swells or rises, or that the improving stratum is deformed depending on properties of the ground 1.
To cope with the drawback, as indicated in inventions of Japanese Patent Application Laid-open Nos.H6-212620 and 6-33446 (Japanese Patent Publication No.H8-30332), and Japanese Patent Application Laid-open No.7-300849 shown in FIGS. 23 and 24, a predetermined antecedent bore 10 is previously formed in the ground 1 by a casing pipe. Improving material transportation passages 16 each having a small diameter and provided at their tip ends with laterally directed ejection ports 15 whose opening positions are different in a longitudinal direction are previously banded together and inserted into the antecedent bore 10 as shown in FIG. 24. The improving material transportation passages 16 are connected to an improving material tank 6 through a valve 17 and a header 18. The pump 5 is connected to the improving material tank 6 through a compressor 19 and a controller 20. A predetermined small amount of an improving material 9 is charged into the ground at a low pressure through a sealing mortar 13 charged in the antecedent bore 10. By charging the improving material 9 through many points by the low pressure penetrance, no crack is generated, and techniques capable of stably improving ground are developed, and some of them have been put to practical use.
However, if the above described charging-through many points is used for the ground improvement technique of transportation passage, since the ejection ports 15 of the improving material transportation passage 16 are offset in a vertical direction and the improving material 9 is supplied under pressure by the single-cylinder pumps 5", the ejection dynamic pressures of the improving material should be different from one another due to the properties of the ground corresponding to the ejection port 15. Instead, an ejection mode by the same dynamic pressure must be employed. Therefore, although there is a merit that the grout 9 as the improving material is charged into a wide improving area through many points simultaneously, there is a drawback in that a difference is generated in the improved degree in the improved area. Further, since the pumping pressures by the single-cylinder pumps 5" are the same, even if the discharge pressures of the pumps 5 are set different, the ejection pressures at all of the ejection ports 15 are basically reach limits, and there is a problem that it is difficult to individually control the ejection ports 15. Further, there is a demerit that even if the discharge pressures are set different depending on differences in depth of the ejection ports 15, there is a limitation in design for setting the ejection pressure from the ejection ports 15 at different values depending on depth.
Although a technique for interposing a pressure pot between the header 18 and the improving material tank 6 is developed, since pressure adjustment by interposing the pressure pot must be conducted for all of the ejection ports 15, it is difficult to adjust the ejection pressure of each of the ejection ports 15 in accordance with the properties of the ground which differ depending on the positions of the ejection ports 15.
Although the system includes the single-cylinder pumps 5", the system itself must includes the compressor 19, the controller 20 and the like, which are expensive. Further, the control, management, and operational maintenance are extremely complicated.
As a conditioner charging pump, although there is a multi-cylinder pump such as three cylinder type, in the present case, the pump only includes a smoothing function in order to avoid a variation in charging operation due to pulsation of conditioner charging by each of the cylinders (or pistons), and there is a demerit that the above prior art does not include a function capable of totally or partially selecting the charging operation through many points, especially through a vast number of points.